Affinity of pulsed positive discharges to dielectrics in N2:O2 mixtures

We simulate positive streamer discharges developing in N2:O2 near dielectric and conductive materials. This research is important, for example, in the high voltage technology where surface flashovers are to be avoided. We designed an axially symmetric model in which a positive inception cloud develops at the tip of the needle electrode and propagates towards and then along a dielectric rod. We measure the velocity of a positive inception cloud (before the inception cloud is destabilized into filaments) propagating along the dielectric rod and compare it with experiments.We also explain the importance of the fact that the photoionization is shaded by the dielectric rod and therefore positive streamers in air are less sensitive to the electron emission from the dielectric surface